1. Field of the Invention
Washing cellulosic wood pulp.
2. Review of the Prior Art
There is a great amount of prior art describing bleaching at low consistencies. None discloses isolating or substantially isolating a stage. Patents describing low consistency ozone stages are Kempf, et al. U.S. Pat. No. 4,080,249 and Eckert U.S. Pat. No. 4,119,486.
An article describing various consistencies is Osawa and Schuerch "The Action of Gaseous Reagents on Cellulosic Materials 1. Ozonization and Reduction of Unbleached Kraft Pulp," TAPPI February 1963, Vol. 46, No. 2, pp. 79-84.
Counterflow washing is disclosed in Rapson U.S. Pat. No. 3,698,995, issued Oct. 17, 1972; in Hisey "Countercurrent Washing in Multi-Stage Bleach Plant Operation at Brown Company," American Paper Industry, September 1969, pp. 43-45; and in Histed and Nicolle, "Water Reuse and Recycle in the D.sub.C EDED Bleach Sequence," and "Water Reuse and Recycle in the C.sub.D EHDED Bleach Sequence," pp. 133-140 and 167-170, respectively of the preprints of the CPPA/TAPPI International Pulp Bleaching Conference given in Vancouver, British Columbia June 3-7, 1973. The three articles do disclose a split washing stream to a washer, but none of these articles disclose isolating or substantially isolating a washing stage.
There have been installations, usually chlorine washers, in which the washing fluid applied to the mat has been split into two different fluids.